The document discusses identifying hotspots, or files that frequently change and are costly to rebuild, in software build processes. It presents an approach that constructs a build dependency graph from the build system, analyzes the graph to determine file change frequency and rebuild costs, and detects hotspots using a quadrant plot that highlights files that change often and have high rebuild costs. Case studies on two open source projects found a small number of hotspot files accounted for a majority of rebuild time. Focusing refactoring on hotspots could significantly improve build performance.